Auditory steady-state evoked responses for preterm and term neonates.

Hearing thresholds were estimated in normal-hearing term and preterm neonates of <35 weeks of age using multiple-stimulus auditory steady-state responses (ASSRs). The tresholds, expressed in decibel sound pressure level, at signal frequencies of 500, 1000, 2000 and 4000 Hz were 44.30 +/- 9.88, 27.80 +/- 6.79, 26.77 +/- 6.09 and 32.87 +/- 6.12 for the term group and 49.11 +/- 9.44, 26.38 +/- 6.59, 26.74 +/- 7.57 and 35.90 +/- 8.23 for the preterm group. Significant threshold differences were measured between the groups at 500 and 4000 Hz, while the thresholds at 1000 and 2000 Hz were similar. The signal and noise levels as well as signal-to-noise ratio of responses were also measured and found to be similar. These results indicate that ASSRs can be effectively measured with a similar signal-to-noise ratio in both groups, but that there is a significant maturational effect occurring during gestation at the level of structures which participate in the formation of the ASSR at 500 and 4000 Hz. Copyright 2009 S. Karger AG, Basel.